Thermal conductivity of solid NaF under high pressure

The thermal conductivity () of solid NaF has been measured over the temperature (T) range 100–350 K and at pressures (P) up to 2.5 GPa, using the transient hot-wire method. Results for (T,P) could be described to a good approximation by the Leibfried-Schlömann formula. It was found that the isochoric temperature derivative of the thermal resistivity W (= ^–1) increased systematically with the mass ratio for the B1-type phases of the sodium and potassium halides.     

Thermal conductivity and heat capacity of synthetic fuel components

As part of a group contribution study on the liquid thermal conductivity of synthetic fuel components, experiments were performed to study the effects of dimethyl and ethyl-group additions to cyclohexane. A transient hot-wire apparatus was used to measure the thermal conductivity of these three fluids between ambient pressure and 10.4 MPa over a temperature range of 300 to 460 K. Thermal conductivities measured with this instrument have been assigned an accuracy of ±2% based upon a standard deviation comparison with a toluene standard established by Nieto de Castro et al. (1986). The thermal conductivities and excess thermal conductivities of the naphthenes investigated have been successfully linearized by plotting the data versus reduced density exponentiated to the power of five. By using data previously reported by Perkins (1983) and Li et al. (1984), this linear reduced density method is demonstrated for methyl, dimethyl, and ethyl additions to cyclohexane, as well as methyl and dimethyl additions to benzene. The naphthenes have been shown to have similar intercepts, with slope changes dependent upon the functional group attached to cyclohexane. The aromatics have a less pronounced slope change with additional functional groups attached to the benzene base. This instrument was also used to determine heat capacities, via the thermal diffusivity, to within ±10%.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

金属氧化物纳米流体的导热性能研究

采用瞬态热线法测量了4种不同种类、不同体积份额配比的纳米流体的导热系数,分析了纳米颗粒属性、体积分数、悬浮稳定性及温度等因素对纳米流体导热系数的影响.实验结果表明,在流体中加入纳米颗粒将显著提高流体的导热系数.     

The thermal conductivity of benzene and toluene

The thermal conductivity of liquid toluene and benzene was measured in the temperature range 298 to 370 K, near the saturation line, using an absolute transient hot-wire technique. The measurements were made in a modified version of an existing instrument, equipped with a new automatic Wheatstone bridge, computer controlled. The bridge measures the time that the resistance of a 7-m-diameter platinum wire takes to reach predetermined values, programmed by the computer. The computer can generate up to 1024 analog voltages, via a 12-bit D/A converter. The accuracy of the measurements with this new arrangement was assessed by measuring the thermal conductivity of a primary standard, toluene, at several temperatures and was found to be of the order of 0.3%. Benzene was chosen because it is under study as a possible secondary standard for liquid thermal conductivity by the Subcommittee on Transport Properties of IUPAC.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity of air in the range 312 to 373 K and 0.1 to 24 MPa

We have used the transient hot-wire technique to make absolute measurements of the thermal conductivity of dry, CO₂-free air in the temperature range from 312 to 373 K and at pressures of up to 24 MPa. The precision of the data is typically ±0.1%, and the overall absolute uncertainty is thought to be less than 0.5%. The data may be expressed, within their uncertainty, by polynomials of second degree in the density. The values at zero-density agree with other reported data to within their combined uncertainties. The excess thermal conductivity as a function of density is found to be independent of the temperature in the experimental range. The excess values at the higher densities are lower than those reported in earlier work.Nomenclature Thermal conductivity, mW · m^–1 · K^–1 - Density, kg · m^–3 - C _p Specific heat capacity at constant pressure, J · kg^–1 · K^–1 - T Absolute temperature, K - q Heat input per unit wire length, W · m^–1 - t Time, s - K(=/C _p) Thermal diffusivity, m² · s^–1 - a Wire radius, m - Euler's constant (=0.5772 ) - p _c Critical pressure, MPa - T _c Critical temperature, K - _c Critical density, kg · m^–3 - R Gas constant (=8.314 J · mol^–1 · K^–1) - V _c Critical volume, m³ · mol^–1 - Z _c(=p _c V _c/RT _c) Critical compressibility factor     

Measurements of the thermal conductivity of aqueous LiBr solutions at pressures up to 40 MPa

This paper describes absolute measurements of the thermal conductivity of aqueous LiBr solutions in the concentration range 5 to 15m (molality), the temperature range 30 to 100°C, and the pressure range 0.1 to 40 MPa. The measurements have been performed with the aid of a transient hot-wire apparatus employing a thin tantalum wire coated with an anodic tantalum pentoxide insulation layer. In using the tantalum wire, a modification of the bridge circuit has been made to keep the electric potential of the wire always higher than the ground level in order to protect the insulation layer from breakdown. The experimental data, which have an estimated accuracy of ±0.5%, have been correlated in terms of the polynomials of concentration, temperature, and pressure for practical use. Also, it has been found that the pressure coefficient of the thermal conductivity decreases with increasing concentrations.     

Thermal conductivity of liquid halogenated ethanes under high pressures

New experimental data on the thermal conductivity of liquid halogenated ethanes, R112 (CCl₂F-CCl₂F), R113 (CCl₂F-CClF₂), R114 (CClF₂-CClF₂), R114B2 (CBrF₂-CBrF₂), and R123 (CHCl₂-CF₃), are presented in the temperature range from 283 to 348 K at pressures up to 200 MPa or the freezing pressures. The measurements were carried out by a transient hot-wire apparatus within an uncertainty of ±1.0%. The thermal conductivity data obtained have been analyzed by means of the corresponding-states principle and other empirical methods. It is found that the corresponding-states correlation =f(T_r, P_r) holds well for R112, R113, and R114. The thermal conductivity can also be correlated satisfactorily with temperature, pressure, and molar volume by a similar expression to the Tait equation and the dense hard-sphere model presented by Dymond.     

The thermal conductivity of toluene and water

A new instrument is presented to measure the thermal conductivity of polar and electrically conducting liquids based on the transient coated hot-wire method. The performance of the apparatus has been assessed with toluene and water, which are recognized as standard reference materials for nonpolar and polar fluids, respectively. New results are reported fort the thermal conductivity of these liquids between 298 and 370 K and at pressures slightly above the saturation. The results show that the instrument is capable of an accuracy better than ±0.5%, while the precision and reproducibility are better than ±0.3%.     

Thermal conductivity of R32 and its mixture with R134a

The liquid thermal conductivity of R32 (CH₂F₂) and R134a (CF₃CH₂F) was measured in the range from 223 to 323 K and from 2 to 20 MPa by the transient hot-wire method. The thermal conductivity of the R32+R134a mixture was also measured in the same range by varying the mass fraction of R32. The measured data are analyzed to obtain a correlation in terms of temperature, pressure and composition of the mixture. The uncertainty of our measurements is estimated to be within ±2%.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Measurement of the thermal conductivity of molten semiconductors

The thermal conductivity of molten InSb in the temperature range between 800 and 870 K was measured by the transient hot-wire method using a ceramic probe. The probe was fabricated from a tungsten wire printed on an alumina substrate and coated with a thin alumina layer. The thermal conductivity was found to be about 18 W· m^–·K^–at the melting point and increased moderately with increasing temperature. The thermal conductivity of alumina used as the substrate for the probe was also measured in the same temperature range.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.On leave from NEC Corporation.     

Thermal conductivity of fourteen liquids in the temperature range 298–373 K

New experimental data on the thermal conductivity of 14 organic liquids at atmospheric pressure are presented in the temperature range from 25 to 100°C. The liquids measured are five n-alkanes (C₆, C₇, C₈, C₁₀, C₁₂), cyclohexane, six aromatic hydrocarbons (benzene, ethylbenzene, o-, m-, p-xylenes, isopropylbenzene) and two phenyl halides (chloro-, bromobenzenes). The measurements were performed by a transient hot-wire method on a relative basis. The thermal conductivity of toluene, which was selected as a reference liquid, was determined on an absolute basis with another transient apparatus. The precision of the present experimental results is within ±1.2%. The uncertainty of the thermal conductivity values is estimated to be within ±2%; this includes the uncertainty of the values of toluene as the reference liquid. The experimental results for each liquid are represented satisfactorily by a linear equation in temperature. At a reduced temperature T/T _c=0.5, thermal conductivity has a simple relation with the molar density for each homologous series of liquids.     

The thermal conductivity and viscosity of benzene

New absolute measurements of the thermal conductivity of liquid benzene are reported. The measurements have been carried out in the temperature range 295–340 K, at atmospheric pressure, in a transient hot-wire instrument. The accuracy of the measurements is estimated to be ±0.5%. The measurements presented in this paper have been used, in conjunction with other high-pressure measurements of thermal conductivity and viscosity, to develop a consistent theoretically based correlation for the prediction of these properties. The proposed scheme permits the density dependence of the thermal conductivity and viscosity of benzene, for temperatures between 295 and 375 K and pressures up to 400 MPa, to be represented successfully by two equations containing just two parameters characteristic of the fluid at each temperature.     

瞬态热线法液体导热系数测试系统的研制

根据瞬态热线法测量导热系数的原理,研制了测量装置和数据采集系统.利用阳极氧化的方式,在热线表面进行绝缘处理,使其能够适用于导电性或者极性物质的导热系数的研究.为了检验该系统的性能,在常温常压下对蒸馏水的导热系数进行了测量.测试结果表明,该系统能够满足导热系数测试的需要.     

Thermal conductivity of argon in the temperature range 107 to 423 K

The thermal conductivity of argon between 107 and 425 K has been measured in a transient hot-wire instrument. The results in the limit zero density have been employed to assess the accuracy of the instrument using exact kinetic theory expressions and has been found to be better than ±0.5%. The data at elevated densities are employed to examine the applicability of the modified Enskog theory in the gaseous phase and the hard-sphere theory in the liquid phase.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

A computer-controlled instrument for the measurement of the thermal conductivity of liquids

A new instrument for the measurement of the thermal conductivity of liquids by the transient hot-wire method is described. The instrument has features in common with earlier versions but employs a novel technique for the determination of the transient temperature rise of the hot wire during the course of a measurement. New determinations of the thermal conductivity of toluene confirm the accuracy of the instrument to be better than 0.5%.     

Thermal conductivity and heat capacity per unit volume of poly(methyl methacrylate) under high pressure

The thermal conductivity and heat capacity per unit volume of poly(methyl methacrylate) (25 and 350 kg · mol^– in molecular weight) have been measured in the temperature range 155–358 K at pressures up to 2 GPa using the transient hot-wire method. The bulk modulus has been measured up to 1.0 GPa at 294 K and yielded a constant valueg = 3.4 ± 0.3 for the Bridgman parameter. No dependence on molecular weight could be detected in the properties we measured.     

Thermal conductivity of the new refrigerants R134a,R152a,and R123 measured by the transient hot-wire method

Thermal-conductivity measurements are reported for the new refrigerants R134a, R152a und R123. Transient hot-wire experiments were performed which cover both the liquid and vapor states at temperatures and pressures ranging from?=?20°C to 90°C and fromp=0.1 bar to 60 bar respectively. The results are correlated with density and temperature. In addition temperature dependent correlations are presented for (i) saturated liquid, (ii) saturated vapor, (iii) ideal gas (which equals approximately vapor state at ambient pressure). Finally the results are compared with data from the literature and also with the thermal conductivities of R12 and R11.     

Thermal conductivity and density of toluene in the temperature range 273–373 K at pressures up to 250 MPa

New experimental data on the thermal conductivity and the density of liquid toluene are presented in the temperature range 0–100°C at pressures up to 250 MPa. The measurements of thermal conductivity were performed with a transient hot-wire apparatus on an absolute basis with an inaccuracy less than 1.0%. The density was measured with a high-pressure burette method with an uncertainty within 0.1%. The experimental results for both properties are represented satisfactorily by the Tait-type equations, as well as empirical polynomials, covering the entire ranges of temperature and pressure. Furthermore, it is found that simple relations exist between the temperature dependence of thermal conductivity and the thermal expansion coefficient, and also between the pressure dependence of thermal conductivity and the isothermal compressibility, as are suggested theoretically.     

Absolute measurements of the thermal conductivity of alcohols by the transient hot-wire technique

New absolute measurements of the thermal conductivity of methanol, ethanol, propanol, butanol, pentanol, and hexanol at atmospheric pressure and in the temperature range 290–350 K are reported. The overall uncertainty in the reported thermal conductivity data is estimated to be better than ±0.5%, an estimate confirmed by the measurement of the thermal conductivity of water. The measurements presented in this paper have been used to develop a consistent theoretically based correlation for the prediction of the thermal conductivity of alcohols. The proposed scheme, based on an extention of the rigid-sphere model, permits the density dependence of the thermal conductivity of alcohols, for temperatures between 290 and 350 K and atmospheric pressure, to be represented successfully by an equation containing just one parameter characteristic of the fluid at each temperature.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

A transient hot-wire method for measuring the thermal conductivity of gases and liquids

In this paper we describe a version of a transient hot-wire apparatus which employs an integrating digital voltmeter to measure the bridge out-of-balance signal. The integrating period of the voltmeter is variable and is routinely set equal to one 60-Hz power-line cycle, 16.67 ms. Use of measurement or integration periods less than an integral multiple of the power-line period results in substantially more electronic noise and a significant degradation in experimental precision. A correction to the working equation which accounts for the integration of the out-of-balance signal is also presented. The precision of the digital voltmeter used with the apparatus is ±0.1 V, which translates into an ultimate precision of ±0.03 mK in the measured temperature rise. In practice the precision in the temperature rise is typically ±0.3 mK, which represents a moderate improvement over the precision generally obtained with transient techniques employing automatic bridge balancing schemes. Although the current apparatus is designed principally for measurements of the thermal conductivity of liquids, it can been used for gas-phase measurements, with some decrease in accuracy due to the somewhat larger heat capacity correction which must be applied to the temperature rise measurements. The operation of the instrument was verified by measuring the thermal conductivities of toluene and nitrogen. Preliminary data are presented for the new environmentally acceptable fluorocarbons such as R-134a (CF₃CH₂F), R-123 (CHCl₂CF₃), and R-141b (CCl₂FCH₃).Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.